I'm on the fence on this one. Here's why. You need a degree of suction for the plaster to adhere to the surface. We were always taught Never to apply PVA too strong i.e.50/50 as it wont penetrate into the background and adhere , it just forms a skin on the surface which can then pull away with the plaster attached to it. The golden rule is to flick some water on the wall and see if it runs to the bottom. If it doesn't then there's still too much suction. I'm not knocking you Kirk as I still think you're a top bloke that does cracking work 👍

Just great listening to a man who know his subject like the back of his hand. The local down to earth dialogue is also music to my ears. Thank you for devoting so much of your own time to help the rest of us. You are a true brick.

In 1985, I used PVA to prime previously painted LBC commons for rendering and Tyrollean finish. In 2023, that surface has no signs of any render falling off. The old lime paint was removed with a spiked wheel “scabbler”machine. It was primed and later rendered with sand cement.

Now that's a turn up for the books. What a great test thanks for doing this Kirk I'm going to have to turn to SBR and ditch the PVA unless I have the time on the job to use stu's mix. Even though stu's mix has really surprised me as it contains cement you would have thought the cement in the mix would have made it high suction. Thanks again for taking the time to do this mate

Mate what a watch that was. My wife thinks I’m sad for being so glued to this experiment. ( no pun intended) I’ve been waiting for this since you did your q and a prior. I’ve learned a lot from this and was all ready in the process of switching to sbr over pva. This experiment has confirmed it’s the right thing to do, thank you so much for the time and effort you’ve put into this. If I could I’d nominate you for a nobel prize for actually adding to sum of humanity’s knowledge here. You’re a legend and I love ya, thanks again mate

I was a plasterer for 20 years, before I moved on. We only had pva , wish they had these other glues 30 years ago. I remember my brother in law who was also a plasterer remembers when there was no such thing as pva.

Nice one Kirk, I'm sticking with SBR :) . SBR mixed with cement is great for sticking sand & cement to low key bricks and blocks inside and out. I always use the off cuts of the drywall beats to stir SBR, they are handy for string paints as well as it goes through the holes and mixes well, I might start selling the bead off cuts on eBay as paint stirrers, this time next year I might be a millionaire ..... keep smiling Kirk 👍

Great test, and it certainly put my mind at ease! Doing a small job plastering a boxed in section under the stairs. Faff having to plasterboard the steps, and a faff to plaster. First timer too. Went against everything said online (I'm also a research scientist, so couldnt understand how SBR would possibly work either), and used sikabond SBR+ neat at per your other two videos on this topic, and by the time I'd mixed up what I'd need it had gone off. Plastered over beautifully, and you could instantly tell where it hadn't been applied when feathering across the new board panels to the old paint. Suction dried the plaster right away. Thanks for giving me the confidence to try this (done most trades as a DIY now) but 100% the hardest one for me. I'm sure practice will get a better finish in future, and even a part worn good quality trowel will only get better in time. Cheers Kirk, keep up the fantastic work 👍🏼

Although not totally scientific I found this a great video. Very informative but I'd have like to have seen one more option. That of just soaking the substrate and then putting the plaster straight on. If the substrate is wet enough it will counter the suction issue to a degree. I'm no platerer but spent years as a bricklayer. One of the issues I saw was when laying engineering bricks they'd often "swim" because (due to their density) they provide very little suction. Instead the water would be separated from the mortar by the weight of the brickwork. This would form a film, allowing for the bricks to just float out of position. Some cowboys would actually just sprinkle neat cement on their mortar bed to counter this, (very poor practice) whereas the correct solution is simply to mix up the mortar quite dry in the first place. We'd encounter the opposite problem in hot weather with regular brickwork. Basically the bricks would soak up too much water. Drying it out before the mortar has a chance to set. This would result in brickwork that looked fine but had no bond between the bricks and the mortar. The remedy in this situation was to just dunk the bricks in water before laying them. Did the job a treat.

Lets face it, the biggest latereral force that will be applied is Blutack, i'll stick to 50/50 PVA as it's never failed externally or internally for me.

SBR is latex-based and ideal for external waterproofing, plastering over it using finish plasters adheres well but will pop at some point due to expansion. Blue grit is much better as a primer as it not only provides a mechanical key but sets like concrete, giving an excellent background for bonding coat and finish plasters. I used to use waterproof PVA for most of the reskims over artex etc as it gives excellent adhesion - providing the plaster goes over it when tacky not dried and water does not soften it as in standard PVA.

Spot on video Kirk, I had this discussion with someone on your video about PVA..and I basically stated the same different primers for different backgrounds setting times ect. your video is the first time I ever seen in all my time on KZfaq...hack even at college way back in 97 no tests like this were ever done to show primers ture capabilities and I'm glad I watched this. I swapped over to SBR..love it found Bulegrit not to my liking from now on I'm going to make up different types for jobs at hand. Your the kind of fella we need on here shouting for our trade Not buy this tool buy that tool it's great im not knocking those types each to Thier own. Yours are just Honest reviews and testing of items showing the good & bad Training the young lads the right way At a time when its more important than ever I love doing domestic work but all to often I'm reskiming, worse cases ripping down and start again stuff less then 10yrs old. For me personally that's a sgin of poor workmanship or lack of training Plastering a trade were theres no place to hide once it's painted Every sperad is only as good as his last job. Repeat work a the only ture test of a real sperad. All the very best best for the future mucka 🍻

0:01 to 44:20 minutes worth watching this man is a LEGEND in the trade and takes pride with his work, Shame not more, but this is why you get to the head table like the John Wick of plastering.

Excellent experimentation. Liked how you dealt with the upsets (like the scales) and the technique for pulling the samples.

That was a fantastic and truly comprehensive product test Kirk, and many thanks for taking the time and effort in putting it all together for us, it’s very much appreciated mate, and I’ve certainly learned a lot from it. Thanks again 😊👍🏴󠁧󠁢󠁳󠁣󠁴󠁿

I loved this video Kirk and really appreciate the time and effort you went to putting this all together. I'm resting a little easier in my bed watching this as 2 days ago I replastered my bathroom ceiling over artex. The artex was well stuck to the bare boards from new (21 year old house) and has only ever been painted with matt emulsion. I gave the artex a really good scrape and a wire brush then SBR,d the sh..the out of it. A 50/50 mix of SBR/water first, allowed to dry then a heavy neat coat of SBR and left to dry for 2 days before I plastered it. I was quite worried as the ceiling looked like it had been varnished by the time the SBR had dried. First time I've used SBR after watching your videos and I thought I'd wrecked the job by over doing it. I skimmed it anyway, 1st coat board finish, 2nd coat 50/50 board/multi as I didn't have quite enough board finish and the suction was zero. I am not a pro plasterer and speed is not my strength, but even I was hanging around waiting for the plaster to firm up (1st time ever..... I'm usually panicking at the first wet trowel stage) and it all seemed to go quite well. But..... I've been worried that the whole lot will shell off when it's dry. More confident now that it won't. Blooming hell though, I will go a bit easier with the SBR next time. I used Sikabond and don't know if it's just me but the stuff stinks horrible 🤮. Thanks again Kirk for a great video.

Big thank you to you both for the time invested

Well, that was interesting! My thoughts, Blue Grit is about half the price of SBR, so more cost effective, maybe a mixture of SBR/Blue grit applied the same day for killing the suction would work! I think Blue Grit helps drag the plaster of the trow better, (not by much though) so less pressure needed to apply the plaster would save a tiny bit of work, every little helps. Mixing SBR with PVA, if that cuts the suction down, it will save on material costs.

Great vid. There is a difference between contolling suction, killing suction and sealing/priming the surface. All of which I use different ratios of pva for. That's the skill and knowledge in my opinion that is misunderstood. Pva manufacturers instructions are a waste of time as well as a 50/50 mix. Every surface requires a different approach in my opinion and watching the pva dry is key to understanding what suction you have. Pva 50/50 never stood a chance against neat sbr or neat blue grit. Also, adding an aggregate decreases the porous surface area. I've always applied pva as neat as possible by adding just a splash of water to make it easier to apply. A second mist coat too can be beneficial. I used sbr on friday for the first time and quickly regretted it. Suction was not controlled and if the sbr gets into the plaster it causes it to drag like a bitch. Reminded me of tilers primer or self levelling primer/sealer and they're specifically designed not to kill suction but to reduce it. After using sbr neat I've now moved onto pva neat and adding 10-20% of sbr and splash of water.......I'll see how that goes on monday. But I'm doubtful It'll be any better than strong pva mix.

Absolutely amazing to see . Especially us plasterers. Always wanted to do a test like this however ive never really had the time. Think you have shed alot of knowledge to people kirk . Cheers mate 👍

I just plastered an Artex ceiling. I used about 2/3rds SBR to water. Rolled on, dead easy. Wait till it goes tacky or dry. Works so well. I used to use PVA and it was crap; things may be different now. Never used grit. SBR for me.

Not a plasterer, but when i did my cellar, i primed with 1:1:1 SBR Cement & Sand (Mix of smooth and rough). Id be tempted to test SBR and Cement on the back of one of theme boards see if you can beat 14kg. Great video!

I’m a novice at this and this test was very interesting to me. I’m currently using PVA but following on from these tests I think that SVR seems to be the safe bet without going crazy. Great experiment :)

Great video as always Kirk! Thanks for the time and effort you put in to this! 👍

I’ve been plastering for 40yrs and 30yrs ago I did a similar test using as a background a previously plastered wall (sand & cement u/c + sirapite B finish, the hardest ) I tested for adhesion by using strips of hessian scrim and yanking them the following day. I found 3:1 water:Unibond PVA on a previously sealed with 5:1 pva worked well provided the 3:1 adhesive coat still had tack. We didn’t have SBR then. Using sharp sand as a grit key mixed with sealant worked but sank to the bottom of the bucket and ended up being dashed on like spatterdash. Nice bit of science there Kirk.

All depends on the quality of PVA you use , There’s a lot of weak crap on the market, Pay extra and use the uni bond brand , I let mine go off and then skim , never any issues, Saying that with re skim it’s all about what’s on the surface your going over and how well adhered that is .

Thanks mate that was an excellent real world test on good tried and tested products. I like how you break things down and make it simple and easy to understand without any bias. I reckon you'll go far keeping it real. Subscribed!

Fantastic comprehensive video Kirk fairplay for putting this together & thank you for testing out my super primer! 😊 SBR PVA & Cement can actually be skimmed after an hour mate if it's hanging just pop the floor fan on for 20 mins 👍 Much cheaper than blue grit too!

Excellent video from an excellent plasterer.Keep up the good work Kirk.👍

We find if we do 2 coats of PVA the day before, letting dry in between coats, we can skim it without any issues at all the next day. The problems always happen when skimming on wet or tacky PVA. We can also get the customer to do the PVA, which saves us time.

Brilliant video. Strangely enjoyed it! Was always a PVA user. Also used bluegrit and had better results and finish in my plastering, again because my PVA was drying out quicker. Will try SBR in future.

Fantastic test...I was curious about SBR applied the day before as many people thought till now (including myself) that when it dries it creates a waterproof layer and plaster doesn't actually adhere to the background but only to that waterproof layer. Your test shows it adheres well to the board itself. Blue grit is a fantastic product but way too messy to work with as are all different mixes just too much hassle and most of the time there is no time to mess about on the job. So yes SBR is probably the best but blue grit is still my choice on artex painted with vinyl silk or any other shiny finish... Thanks for doing that Kirk 👍

Brilliant test you need to do over silk and artex next high gloss paint

Shud have done 1 just plaster directly on board but gauge in with trowel like tile adhesive then go over and flatten rather than just coat on and flatten makes better contact adhesion worth a try

Cracking test mate and just confirms to me was the right decision ditching the PVA, definitely settles a few unknown questions on how good SBR actually works 👌🏼

A lot of time and effort gone into the video cheers mate. Don’t think the holding experiment gave us much feedback though, think that was measuring the strength of the scrim rather than the adhesion. A scraper test would of been more beneficial.

That was enjoyable watching well done big man 👍

Hi Kirk, what a really interesting Test to do. Thank you for your time and effort in doing the video ..👍👍

i can feel a nobel prize coming for taking the scientific method to new heights well done sir

Ive always used sbr & cement to tank garden walls before rendering... Good vid 👍

I've been using SBR for years. Don't forget with pva . One coat going over where it sucks in while im putting that one coat on - done . Also, no need to remove woodchip wallpaper! Proven ;-)

I sometimes put pva in my skim mix aswell.

Hi kirk i have been Plastering since i was 16 I'm now 34 started of pva and moved to gritted products after seeing this video sbr seems to be a clear winner in my eyes for speed ..👍

This is really interesting, I would like to see PVA and a handfull of multifinish and PVA and cement vs SBR and multifinish vs SBR and cement!

Thank you for this video - alot of TLC has gone into this and you’ve just shown how crazy the results are. SBR for me, win win. Cheers for all your vids - absolutely hooked on them!!!

now this is what we should be learning in scool legit experiments and can be applied in real

Love your videos by the way ! In the pvas defence i would say give it another coat as cement board has such a high suction and if would probably fair better especially as its the cheapest product and less hustle as some of the methods involve mixing other products together.

Great video Kirk. Thank you for your time and educating us

Thanks for your time & effort in making this video. Many things there to take on board & consider. Well done.

Great video mate, loads of decent Info here - I have used grit several times but 95% of work has always just been PVA mix

What is the cost comparison for each one?

Great video, I couldn’t stop watching!! Interesting results, nice one Kirk

Brilliant. I have been looking forward to seeing this. Thanks Kirk.

This test will go down in history mate 👏🏻

I've never had a problem with pva in 44 years.

I served my time as a Qualified plasterer and I know that you know what your talking about..

3/4 of the walls and ceilings in London are stuck together with PVA and a prayer....😅

You should also try Parex micro gobetis and Knauf beton kontact or the spraykontact is even better if you can get hold of it in the uk. I've used the knauf stuff for years working in Holland but recently came back to uk. A friend recommended the Parex micro gobetis for artex ceilings, i use it all the time now! The suction is comparable to skimming boards and it also has a grit in to key. Its waaay easier to roll on compared to blue grit cos you can water it down quite a bit and it still works great. The knauf spraykontact is like painting emulsion and can be used on any surface and like the name suggests, it can also be sprayed on with an airlash machine for large areas

Great video loved it . 40 mins of pure entertainment

Love the videos so in depth and informative 👌 awesome work

Would love to see some tests on non porous backgrounds. Eggshell/gloss walls or pvc or something

3quater pva 1quater water apply and let fully dry, and skim over in my 20 yeast experience I find best and would use in my own house.

Hi. Thanks for this video. It's great knowledge to have. I'm still using pva for the most part but do use sbr when I feel it's required. Keep up the good work.

A decent comprehensive test you did there mate, nice one 👍🏻

was so interested in this kirk...great test,you got patient's mate..very interesting about pva, but like you said the plaster doesn't need to hold weight, and sometimes you use suction to your advantage too,so..horses for corses aye.

This is gold kirk and also one of the reasons I bizarrely choose to spend hours watching an overweight middle aged bloke plastering walls on youtube! 😘 These comparison tests are what people will keep searching for and viewing in years to come. You should also do a test to see if theres any differences on different brands of plasterboard, another one comparing board finish to multifinish and another skimming a wall with a brand new trowel vs a worn in one!

this was a very interesting video Kirk...keep them coming mate!

Very interesting experiment mate. Thanks for sharing the knowledge.

That was great thanks always wanted to know the differences

Massive Thanks mate,this has been the best video I’ve watched on you tube 😁👍

My old uncle Chris, a cracking plasterer, always said to me uneven suction is the plasterers enemy

Awesome video. Although I think the test needs to be done on a low suction background (painted plaster) because let’s be honest that’s we we use these primers for most. All I care about is adhesion. We now know what gives the best adhesion for ultra high suction background but what about low. Come on Kirk, get your lab coat back on and do the test boy 😂! I was always a 50/50 PVA man but I have an open mind.

Really enjoyed that , I’ve been using pva and gypbond for nearly 28 years lol, definitely going to try out SBR the same day . Would have been nice to see how gypbond faired up for the money it costs .😂 cheers 🥂 Kirky lad .

You should have a laboratory coat on

Great video, well done!!

before looking at comments or watching vid my favourite would be 2 coats of blue grit left overnight simple

@On The Trowel ... The Only thing you Never tried was *""Size"". * (Like in ancient times Cow Dung was used to stop Soot coming through plaster), I believe a form of Size (made from the melted hooves of horses), was used as Suction killing Adhesive... Possibly mixed thinly mixed with Calcium oxide (for a quicklime over skim). If you want to know how I know that? I'm sure I remember it from collage. I served 5 years learning Plastering... My late father (god rest his soul), at one point, had a Plastering, Screeding and Granolithic Floor laying company. Arguably the biggest in the Midlands. Definitely the biggest in the East Midlands. ... I found this video *VERY Entertaining...!* I'm really glad I stumbled across your channel. I've subbed too... And don't worry, if I see you make One Mistake ? *"I'LL JUMP ON YOU...!"* L🤣L (only kidding)...

Would also be really good to see the exact same test on plasterbaord as this is what most of us plaster over . Maybe another video isea sometimes kirk ? 😉

I'm also surprised you didn't water down the sbr since lots of plasterers use 4:1 as per the majority of manufacturers guidelines. This would've been a direct fair comparison with pva. Pva can be applied neat on shiny non porous surfaces as per manufacturers guidelines. But I can't see that SBR is recommended to be used neat. The reason for that may be that if the sbr forms a dry skin it may reduce the bonding strength of the adhesive/plaster or render etc since it's not able to key itself to the substrate.

Is there anything wrong with just dampening a high suction substrate with water?

Good video M8 👏👏👏

Great experiment mate and it was interesting to watch. But I think whilst the results are probably mostly true they're not entirely conclusive. For one, all pva is not the same. I remember when you had to literally squeeze the tub to get the stuff out (yours appears to be Sika which is actually one of the thickest still around) but nowadays with a lot of brands it pours out like it's already mixed. So saying 50/50 will only be representative of the brand you used. It might be completely different for someone using a different brand. Also, maybe you could have put stop bead all around the board to ensure even thickness on the panels. Plus, I've never seen blue grit applied that well in a real live scenario, especially when a clueless labourer has done it 🤣. But all that aside you did a great job with the experiment and as I said it's probably mostly correct anyway. God, I hate going over blue grit. You have to lay it on thick to get over the clumps of grit and there's no suction so it goes ripply.....right where's my sponge float🤣

Hi.Thank you for the video. I found it work a lot better if to mix sand with pva and tiny bit of water.Another two thing to try is what I use sometime is pva and bonding coat, and pva and plasterboard adhesive.

One coat of Pva never had a chance on cement board

what SBR stands for ?

Valuable work, cheers!

Hi Kirk I would like to come up and spend a day on the trowel with you messing up one of your jobs. I think I could learn something from you and we would make a good video.

Hi kirk, great channel. I am just a DIYer but have already learned loads from you so thanks for sharing your knowledge. I once had a room skimmed by a professional, but the paint roller peeled the skim off. Would that be because he used pva and not SBR? Or maybe the mix was too weaK? He used pva ans water on the same day he plastered. Cheers

I think with cement board it would need more than one sealer of pva, so not fair on pva

Lol love the can of beer in the background 😂😂😂 proper builder 😂

Kirk, excuse my ignorance but what is SBR and what does it stand for?

Sbr all the way, love that stuff

Nice one Kirk couldn’t wait for this video!🍻

Great test! Important work your doing on our behalf 👍 liked and subscribed

Great video, I'm thinking SBR and cement though..🤔 Who needs PVA🤷‍♂️

What a happy bear and good plasterer, I’d have a pint with ya mate, probably several… then a shot, then a product test. Lol 😂

Entertaining and informative

Brilliant bud thanks for taking the time and effort to do this test👍

Very interesting………,

When grit first came out ( think it was thistle bondit first?) . It was about 64 quid a tub. I use the febond blue grit mixed with some pva these days. But back then ,no way I was springing for the 64 quid. I used to use almost neat pva mixed with carlite bonding. The lightweight aggregate in bonding gave a good key and seemed to spread pretty evenly if you mixed it every 10mins or so. Bloody messy but aren't they all